1. Field of the Invention
The present invention relates to optical attenuators, and particularly to a loop-back attenuator used for testing optical equipment either prior to installation or after installation.
2. Description of Prior Art
Optical fibers are utilized to transmit optical signals among various items of optical equipment in optical communications systems. Testing of the items of optical equipment is necessary to assure proper functioning. In testing, test conditions must accurately simulate the anticipated operating environment. In operation, optical communications systems generally experience unavoidable attenuation in the optical fibers. That is, loss of optical power transmitted through the fibers. Such systems are specified in terms of maximum optical attenuation that can occur between transmitting and receiving devices while still providing information transfer with substantially no error. Typically, an emitter and a detector of an item of optical equipment to be tested are connected to a device that simulates the optical system that the item of optical equipment is intended to be installed in. The device simulates the system""s characteristic attenuation, among other things.
Loop-back attenuators are used to provide a communication signal path that forms a loop from the emitter to the detector of the same item of optical equipment. Optical signals transmitted from the item under test are looped back to that same item and internally transmitted among its component parts. Consequently, communication from a transmitter to a receiver within the item of equipment can be accomplished without operation of other items of equipment. The loop-back attenuators simulate a loss of signal intensity expected of a communications system in which the item is to be installed for xe2x80x9con-linexe2x80x9d operation.
Referring to FIGS. 1 and 2, a loop-back attenuator 1 disclosed in U.S. Pat. No. 4,952,798 comprises an upper cover 11, a lower cover 12, a screw nut 13, an optical fiber 14 and two optical fiber connectors 15. Each optical fiber connector 15 comprises a ferrule 151 for retaining a distal portion of the optical fiber 14. The optical fiber 14 is formed as a loop, and a film 152 is formed on an end surface of the optical fiber 14. The loop and the film 152 provide controlled attenuation of optical power. The upper and lower covers 11, 12 cooperate to define a space for accommodating and securing the optical fiber 14 and the optical connectors 15 therein. The upper and lower covers 11, 12 are attached to each other and fastened by the screw nut 13. Unfortunately, the film 152 needed for attenuation increases costs. Furthermore, manufacturing of the attenuator 1 is unduly time-consuming. U.S. Pat. No. 5,475,781 also discloses the attenuator.
In view of the above, an object of the present invention is to provide a loop-back attenuator having a bent optical fiber which provides desired attenuation.
In order to achieve the object set above, an optical loop-back attenuator in accordance with the present invention comprises a frame, a cover attached to the frame, an optical fiber, an optical fiber fixture retaining and fixing the optical fiber, and two subscriber connector (SC) plug connectors receiving and retaining opposite ends of the optical fiber therein. The frame and the cover cooperate to fittingly receive the optical fiber, the optical fiber fixture and portions of the SC plug connectors therein. The optical fiber has a bent part which is configured to be semicircular or to have another suitable shape that achieves a desired attenuation.